Our goal is to understand the molecular interactions that regulate the immune response during graft rejection. Multiple studies indicate that graft rejection is complex, polygenic and poorly understood. To investigate the network of molecular interactions that regulate rejection, in this proposal we apply a systems biology analysis to a well-characterized model of transplantation. Using a murine model of heart transplantation, our preliminary data demonstrate that a deficiency of graft produced IL-6 approximately triples graft survival. Graft produced IL6 overcomes suppression by regulatory T cells, and promotes the activation of CD4 and CD8 T effector cells. Thus, graft-produced IL6 functions as a molecular trigger that modulates multiple components of the immune response following transplantation. The experimental approach designed by our laboratory to investigate this complex process has 2 complementary components. First, we will investigate an important observation (prolongation of graft survival due to a deficiency of graft-produced IL-6) in an established solid organ transplant model (murine cardiac transplantation). Second, we will apply state of the art microarray technology, bioinformatics, biostatistics, and systems biology to construct and analyze global molecular models of the regulatory interactions and signal transduction pathways modulating rejection. Our preliminary data and recent publications establish that we can successfully perform these studies. Thus, we propose that applying a systems biology approach, which is the backbone of this application, is appropriate, timely, and synergistic with conventional approaches, to increase understanding of the rejection response. Our overall biological hypothesis is that injury to graft tissue induces IL6 secretion, which functions as a systemic danger signal to activate peripheral immune cells. We will employ both reductionist and systems approaches to address these questions. In Aim I, we will identify candidate signal transduction pathways modulated by graft-produced IL-6 following transplantation. In Aim II, we will predict biological responses for targets of knockdown experiments with RNAi using subnetworks and signal transduction pathways. We anticipate that our systems based approach will provide novel insights into the regulation of immune responses following transplantation and has the potential to identify new therapeutic strategies to prevent the rejection of grafted organs. PUBLIC HEALTH RELEVANCE: We will investigate the immune mechanisms that may be important in determining whether a transplant is accepted or rejected by the patient. We are focusing on interleukin-6 (IL- 6), a cytokine with diverse functions. We have found that IL-6 produced by the donor graft accelerates rejection of the graft. In addition to IL-6, we will analyze immune genes and pathways using microarrays and construct biological interaction networks using systems biology methods to investigate the signals that promote rejection.